tst_qobjectrace: fix potential UB (something with pointers and new)

The current [basic.life] wording seems to cover the existing code, but
IIRC, older versions of [basic.life] were not so relaxed. In
particular, while not completely pertinent, the second placement new
is awfully similar to http://eel.is/c++draft/ptr.launder#example-1

Just make all of this SEP and use std::optional. That way, the code
gets simpler, too, plus we get rid of the last use of C++23-deprecated
std::aligned_storage.

The reset() before the 2nd emplace() isn't necessary, but, in a test,
it doesn't hurt, either, and keeps code readers from guessing whether
the first-emplaced object's dtor is actually properly run (it is).

Pick-to: 6.3 6.2
Fixes: QTBUG-99122
Change-Id: If31a46f8be3a74499f1176133029d097faf7dfe9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 7 insertions, 11 deletions

diff --git a/tests/auto/other/qobjectrace/tst_qobjectrace.cpp b/tests/auto/other/qobjectrace/tst_qobjectrace.cpp
index 093b4d2476..55ab6356cd 100644
--- a/tests/auto/other/qobjectrace/tst_qobjectrace.cpp
+++ b/tests/auto/other/qobjectrace/tst_qobjectrace.cpp
@@ -32,6 +32,8 @@
 
 #include <QtTest/private/qemulationdetector_p.h>
 
+#include <optional>
+
 enum { OneMinute = 60 * 1000,
        TwoMinutes = OneMinute * 2 };
 
@@ -347,17 +349,13 @@ void tst_QObjectRace::blockingQueuedDestroyRace()
 
     while (iteration++ < MinIterations || !timer.hasExpired()) {
         // Manually allocate some storage, and create a receiver in there
-        std::aligned_storage<
-                sizeof(BlockingQueuedDestroyRaceObject),
-                alignof(BlockingQueuedDestroyRaceObject)
-            >::type storage;
+        std::optional<BlockingQueuedDestroyRaceObject> receiver;
 
-        auto *receiver = reinterpret_cast<BlockingQueuedDestroyRaceObject *>(&storage);
-        new (receiver) BlockingQueuedDestroyRaceObject(BlockingQueuedDestroyRaceObject::Behavior::Normal);
+        receiver.emplace(BlockingQueuedDestroyRaceObject::Behavior::Normal);
 
         // Connect it to the sender via BlockingQueuedConnection
         QVERIFY(connect(&sender, &BlockingQueuedDestroyRaceObject::aSignal,
-                        receiver, &BlockingQueuedDestroyRaceObject::aSlot,
+                        &*receiver, &BlockingQueuedDestroyRaceObject::aSlot,
                         Qt::BlockingQueuedConnection));
 
         const auto emitUntilDestroyed = [&sender] {
@@ -379,15 +377,13 @@ void tst_QObjectRace::blockingQueuedDestroyRace()
         // - the metacall event to be posted to a destroyed object;
         // - the metacall event to be posted to the wrong object.
         // In both cases we hope to catch the race by crashing.
-        receiver->~BlockingQueuedDestroyRaceObject();
-        new (receiver) BlockingQueuedDestroyRaceObject(BlockingQueuedDestroyRaceObject::Behavior::Crash);
+        receiver.reset();
+        receiver.emplace(BlockingQueuedDestroyRaceObject::Behavior::Crash);
 
         // Flush events
         QTest::qWait(0);
 
         thread->wait();
-
-        receiver->~BlockingQueuedDestroyRaceObject();
     }
 #endif
 }